Mechanism of the hydration of carbon dioxide: direct participation of H2O versus microsolvation

Thermochemical parameters of carbonic acid and the stationary points on the neutral hydration pathways of carbon dioxide, CO 2 + nH 2O --> H 2CO 3 + ( n - 1)H 2O, with n = 1, 2, 3, and 4, were calculated using geometries optimized at the MP2/aug-cc-pVTZ level. Coupled-cluster theory (CCSD(T)) energies were extrapolated to the complete basis set limit in most cases and then used to evaluate heats of formation. A high energy barrier of approximately 50 kcal/mol was predicted for the addition of one water molecule to CO 2 ( n = 1). This barrier is lowered in cyclic H-bonded systems of CO 2 with water dimer and water trimer in which preassociation complexes are formed with binding energies of approximately 7 and 15 kcal/mol, respectively. For n = 2, a trimeric six-member cyclic transition state has an energy barrier of approximately 33 (gas phase) and a free energy barrier of approximately 31 (in a continuum solvent model of water at 298 K) kcal/mol, relative to the precomplex. For n = 3, two reactive pathways are possible with the first having all three water molecules involved in hydrogen transfer via an eight-member cycle, and in the second, the third water molecule is not directly involved in the hydrogen transfer but solvates the n = 2 transition state. In the gas phase, the two transition states have comparable energies of approximately 15 kcal/mol relative to separated reactants. The first path is favored over in aqueous solution by approximately 5 kcal/mol in free energy due to the formation of a structure resembling a (HCO 3 (-)/H 3OH 2O (+)) ion pair. Bulk solvation reduces the free energy barrier of the first path by approximately 10 kcal/mol for a free energy barrier of approximately 22 kcal/mol for the (CO 2 + 3H 2O) aq reaction. For n = 4, the transition state, in which a three-water chain takes part in the hydrogen transfer while the fourth water microsolvates the cluster, is energetically more favored than transition states incorporating two or four active water molecules. An energy barrier of approximately 20 (gas phase) and a free energy barrier of approximately 19 (in water) kcal/mol were derived for the CO 2 + 4H 2O reaction, and again formation of an ion pair is important. The calculated results confirm the crucial role of direct participation of three water molecules ( n = 3) in the eight-member cyclic TS for the CO 2 hydration reaction. Carbonic acid and its water complexes are consistently higher in energy (by approximately 6-7 kcal/mol) than the corresponding CO 2 complexes and can undergo more facile water-assisted dehydration processes.     

Hydrogen‐bonded chains in three cis‐dichloridoplatinum(II) complexes bearing piperidine and amine ligands

The crystal structures of cis‐dichlorido(ethylamine‐κN)(piperidine‐κN)platinum(II), [PtCl₂(C₂H₇N)(C₅H₁₁N)], (I), cis‐dichlorido(3‐methoxyaniline‐κN)(piperidine‐κN)platinum(II), [PtCl₂(C₅H₁₁N)(C₇H₉NO)], (II), and cis‐dichlorido(piperidine‐κN)(quinoline‐κN)platinum(II), [PtCl₂(C₅H₁₁N)(C₉H₇N)], (III), have been determined at 100 K in order to verify the influence of the nonpiperidine ligand on the geometry and crystal packing. The crystal packing is characterized by N—H...Cl hydrogen bonding, resulting in the formation of chains of molecules connected in a head‐to‐tail fashion. Hydrogen‐bonding interactions play a major role in the packing of (I), where the chains further aggregate into planes, but less so in the case of (II) and (III), where π–π stacking interactions are of greater importance.     

Chemical Constituents and Cytotoxic Activities of Stem Bark of Dialium cochinchinense

Chemistry of Natural Compounds -     

Synthesis and Crystal Structures of Dioxomolybdenum(VI) Complexes with ONS-Donor Ligands

Abstract  

Three dioxomolybdenum complexes namely dioxo(5-chlorosalicylaldehyde thiosemicarbazonato) dimethylsulfoxide molybdenum(VI) (C1), dioxo(5-chlorosalicylaldehyde 2-ethylthiosemicarbazonato) dimethylsulfoxide molybdenum(VI) (C2) and dioxo(5-chlorosalicylaldehyde N-phenylthiosemicarbazonato) dimethylsulfoxide molybdenum(VI) (C3) were prepared. The compounds all crystallize in the triclinic space group P-1 with a = 7.3184(3) ?, b = 7.5035(3) ?, c = 14.9713(6) ?, α = 85.005(2)°, β = 85.616(2)°, γ = 66.987(2)° for C1, a = 8.2339(1) ?, b = 10.1739(1) ?, c = 10.4017(1) ?, α = 78.486(1)°, β = 89.312(1)°, γ = 81.730(1)° for C2, a = 7.0591(1) ?, b = 9.5603(1) ?, c = 14.5762(2) ?, α = 76.280(1)°, β = 81.351(1)°, γ = 81.985(1)° for C3. In general, the overall geometry of these complexes can be regarded as a distorted octahedron with the tridentate thiosemicarbazonato ligands (L²⁻) bonded to the MoO₂ ²⁺ core, with the imine nitrogen, phenoxyl oxygen, sulfur atom and one of the terminal oxygen atoms of the dioxomolybdenum occupying the equatorial position. The sixth coordination site is occupied by the dimethylsulfoxide (DMSO) solvent molecules. The adjacent molecules of C1 are linked by N–H···N intermolecular hydrogen bonding, forming polymeric chains that run parallel to the bc plane. On the other hand, C2 is a discrete molecule while the molecules of C3 associate via weak N–H···O hydrogen bonding interaction to form a polymeric chain that runs along the a-axis.     

Incipient plasticity during nano-scratch in Ni3Al

The subsequent sliding behaviour of the initially elastic, submicron contacts between a diamond tip and bulk polycrystalline Ni₃Al was investigated by nano-scratch tests. Scratches are made under constant normal loads otherwise too low to trigger crystal plasticity in uniaxial nanoindentation experiments. Three types of behaviour are observed: (i) the entire scratch is purely elastic with a sliding coefficient of friction (μ) of about 0.086; (ii) a sudden strain burst in the normal direction, commonly known as pop-in, occurs at the onset of sliding and the subsequent sliding is plastic with μ typically a few times larger than 0.086; and (iii) an intermediate case in which the scratch is initially elastic followed by a pop-in beyond which the sliding becomes plastic. The intermediate case occurs rather randomly. The μ for elastic sliding is found to be load- or size-independent, but that for plastic sliding exhibits a strong size effect, i.e. it is small at small loads, but increases towards a steady value at larger loads.     

Probing neutrino and Higgs sectors in $$\text{ SU(2) }_1 \times \text{ SU(2) }_2 \times \text{ U(1) }_Y $$ model with lepton-flavor non-universality

The neutrino and Higgs sectors in the \(\text{ SU(2) }_1 \times \text{ SU(2) }_2 \times \text{ U(1) }_Y \) model with lepton-flavor non-universality are discussed. We show that active neutrinos can get Majorana masses from radiative corrections, after adding only new singly charged Higgs bosons. The mechanism for the generation of neutrino masses is the same as in the Zee models. This also gives a hint to solving the dark matter problem based on similar ways discussed recently in many radiative neutrino mass models with dark matter. Except the active neutrinos, the appearance of singly charged Higgs bosons and dark matter does not affect significantly the physical spectrum of all particles in the original model. We indicate this point by investigating the Higgs sector in both cases before and after singly charged scalars are added into it. Many interesting properties of physical Higgs bosons, which were not shown previously, are explored. In particular, the mass matrices of charged and CP-odd Higgs fields are proportional to the coefficient of triple Higgs coupling \(\mu \). The mass eigenstates and eigenvalues in the CP-even Higgs sector are also presented. All couplings of the SM-like Higgs boson to normal fermions and gauge bosons are different from the SM predictions by a factor \(c_h\), which must satisfy the recent global fit of experimental data, namely \(0.995<|c_h|<1\). We have analyzed a more general diagonalization of gauge boson mass matrices, then we show that the ratio of the tangents of the W–\(W'\) and Z–\(Z'\) mixing angles is exactly the cosine of the Weinberg angle, implying that number of parameters is reduced by 1. Signals of new physics from decays of new heavy fermions and Higgs bosons at LHC and constraints of their masses are also discussed.     

Activation detection in event-related fMRI data based on spatio-temporal properties.

Template-based activation detection methods, such as cross-correlation, could be difficult to apply in event-related functional MRI data because accurate a priori knowledge about the activation signal patterns is often not available. As a result, several categories of template-free data analysis techniques have been introduced in the fMRI literature. One previously described template-free activation detection technique is based on the feature that activated voxels yield reproducible time course patterns as the subject undergoes the same simulation in repeated epochs. In this paper, spatial information is incorporated as a second feature and a combined univariate measure is formed. The resulting method is shown to offer measurable improvement in detecting activation regions in simulated data in a highly computationally efficient manner. Its practical utility is demonstrated with an experimental data set obtained with a visually guided motor paradigm.     

The positive maximum principle on symmetric spaces

Positivity - We investigate the Courrège theorem in the context of linear operators that satisfy the positive maximum principle on a space of continuous functions over a symmetric space....     

ChemInform Abstract: Experimental Detection and Theoretical Characterization of Germanium‐Doped Lithium Clusters LinGe (n = 1—7).

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